Process for the treatment of silicates with acids in order to obtain their soluble salts



Oct. 9, 1934. F. JOURDAN 1,976,564

PROCESS FOR THE TREATMENT OF SILICATES WITH ACIDS IN ORDER TO OBTAINTHEIR SOLUBLE SALTS Filed March 10, 1933 Patented Oct. 9, 1934 PROCESSFOR THE TREATMENT OF SILI- CATES WITH ACIDS IN ORDER TO OBTAIN THEIRSOLUBLE SALTS Flix Jourdan, Rome, Italy Application March 10, 1933,Serial No. 660,252

In Italy March 18, 1932 1 Claim.

It is known that many silicates, mainly those containing alkali metals(potassium, sodium, lithium) may be attacked at high temperature andunder pressure by the vapours of volatile acids,

5 such as hydrochloric or nitric acid. When the attack is efiected withthe vapours at high temperature of these acids, which may also be mixedwith water steam, a liquid condensate is obtained which contains insolution the soluble salts resulting from the reaction, theconcentration of the said solution being however slight, which rendersin practice the process very costly and consequently unsuitable, as itwould require to be repeatedly applied or prosecuted by renewingcontinuously the vapours of the acid used in order to exhaust completelythe minerals subjected to the treatment.

The present invention has for its object a new method for effecting theabove said treatment, which allows to obtain with a small expense and ina practical and very convenient way, highly concentrated solutions ofthe salts resulting from the attack of rocks such as leucite, and othersimilar silicates, even with the condensable vapours of active liquids,which in consequence of the attack are but slightly charged with thesoluble salts formed or dissolved.

The principle on which the working of the process according to thepresent invention is based, 3 is the following: After the attack at hightemperature and pressure of the rock under treatment, either alone or inthe presence of other substances capable of facilitating the reaction,and after collecting the liquid condensate or the liquid dropping downmechanically, instead of attacking the rock with the vapour from anotherliquid, the vapour obtained by re-evaporating the condensed liquid, isused; such vapour being pure as it consists only of vapour of acid andwater steam, the dissolved substances in the liquid, in the caseconsidered, being all fixed substances, so that the second attack hasthe same effect as if fresh vapours and steam were used. The condensedvapour contains other substances dissolved in it which increase theconcentration of the liquid, the said operation being continued thusenriching successively the liquid until the complete exhaustion of allthe useful components of the rock has been reached.

In. practice, it has been found convenient to use a quantity of liquidwhich is sufficient to extract from the rock and to transfer into thesolution all the salts obtainable from the rock under treatment, tomaintain the liquid always at the boiling temperature and underpressure, and the charge of rock to be treated at a temperature eitherequal (when wet vapours are used) or slightly lower, so that the vapourcoming in contact with it may condense, both the liquid and the mineralbeing enclosed in the same closed container, having such dimensions thatthe liquid may not reach or come in contact with the material placedabove it.

Under the said operating conditions, the process can be carried out in acontinuous manner, and when good care is taken for thermally insulatfngthe whole apparatus, in order to prevent heat losses, the consumption ofcombustible will be very small, viz: just the quantity which issufl'lcient to replace the heat lost owing to the slight decrease of thetemperature of the charge under treatment, whenever it is necessary todecrease the temperature of the said charge.

The annexed drawing shows schematically a vertical section of theapparatus used for carrying the invention into practice.

Supposing, by way of example, that it is desired totreat the leucitewith nitric acid so as to obtain potassium and aluminium nitrates, theoperation 0 is carried out asfollows:

The leucite is firstly ground or granulated and then placed in acontainer 1 perforated at the bottom and uncovered at the top. The saidcontainer is then introduced into the higher portion a of an autoclaveformed by a vertical tube 2 capable of withstanding the pressure. Theheight of the autoclave must be sufficient to allow that, upon havingpoured into it the liquid required for the reaction, which collects atthe bottom and which in the present case is nitric acid, in a quantityslightly less than that indicated by theory, the said liquid does notreach the vessel containing the charge of leucite, which is placed intothe upper portion of the tube 2. The tube must be made with a materialcapable to withstand the action of the reagents used and of the reactionproducts, or it must be eventually lined with a. material which is notattacked by the said reagents and reactionproducts, such as for examplegrit sandstone. V

Theqautoclave is provided in its lower part with a discharge cock 4 forthe exit of the saturated liquid. The fresh liquid is introduced fromthe top cover 3 through a suitable inlet.

Afterthe autoclave has been charged as described, it is closed, and theliquid, which is collected at its bottom, is heated in any convenientway, such for example, by means of an electric through a pipe having aninlet '7 and an outlet 8,

which causes the condensation of the vapour, which condensed vapourdrops through the underlying layer of leucite from which it drops againto the bottom of the autoclave where it rejoins "described, isintroduced into the apparatus, the

the boiling liquid.

In practical working the cooling above mentioned is not required whenthe steam is already saturated with moisture as is the case in theapparatus now described. I As nitric acid boils at a temperature whichis lower than the boiling point of water, there will? be produced, underpressure and at hightemperature, vapours rich in nitric acid andwater,which will pass through the mass of leucite from the bottom to the topor conversely and the salts formed'remain dissolved in the condensedliquid, falling to the bottom of the autoclave where the nitric acid iscollected. I II I I If the temperature of the attack is kept above 1000., the silica is no longer dissolved and does not assume the gelatinousform which causes the obstructions occurring in the masses of theattackwhen operating with no pressure apparatuses. In addition, the heat,developed during the reaction of the attack in a closed apparatus, maybe utilized wholly or in part for the heating required after-startingthe operation. I i

.Moreover, if the temperature iskept' higher than 125 0., the followingadditional advantage is obtained: it is known that iron nitrate decomposes at a temperature .oiri25" C., while the aluminiumnitr'ate requiresfor its decomposition a a temperature of at least 140 C. ThereforabyWorking at an intermediate convenient'temperature, between the twolimits above mentioned, it will thus be possible to'eliminate' thegreater por- I tion of the iron present in the form of iron oxide whichprecipitates with the insoluble residue. The above described resultcould not be obtained boiling temperature is a function of the concen'trationof the solution in acid and in salts, which varies continuouslyand consequently the temperature cannot be regulated, The boiling actionagitates the maSsQwhile with the operation made under pressure with theacid in vapour form, the desired ,efiect'of dissolving rapidly thepotash and the alumina is obtained directly and in a very simplemannenby operating'atv s'ucha temperature that neither the iron nor thesilica may pass into solution. 1

' If a small quantity of iron, coming from the leucite or from theeventual corrosiori'of the ma- 'terial of the apparatus, should passinto the solution, there maybe added in the solutionfkept underpressure, a precipitant for the iron, such for example potassiumferrocyanide, or any other suitable reagent. The precipitate isseparated from the liquid by filtration, for'example iby passing thesolution through a layer 'o'f'silica formed with the exhausted leucite,which latter thus serves no'longer to eliminate the silica, which withthe process described is produced in the insoluble form, but iteliminates the iron which has passed inthe; solution in the form ofnitrate.

ldrawingthe c'oncentratedliquid free from-acid,

The iron precipitate may on the other hand be eliminated by using anyother of the methods of filtration generally known, or by means of acentrifugal machine, or by any other method known and used in theindustry for separating solid substances held in suspension in liquids.

When'theattack'has been completed, the exhausted leucite is removed fromthe hot apparatus, and another quantity of fresh leucite contained in.another container similar to that above autoclave is then" closed, andthe heat is maintained by producing vacuum in it, so that the water inexcess may be distilled up to the amount I which is considerednecessary, passing the water vapour through the leucite. By operating inthis way the last-traces of free acid which may still be presentin thesolution become fixed, while the distilled water exhausted is free fromacid solution of potassium and aluminium nitrates,

free from iron and from silica, from which the said two'nitrates can beseparated by any known methods, subsequently admitting a fresh charge ofacid into the autoclave. I 1

The operation carriedout as above described allows toleiiect the rapidattack of the leucite, to obtain the complete fixing of the acid withoutany loss, and also the'complete purification of the liquid whichis freefrom silica and from iron, as well asits. concentration by eliminatingfrom ft'the pure water without the .use of pumps or of other costly andcomplicated distilling apparatuses. I V

I claim; I The process of treating silicates with acid vapours at hightemperature for extracting therefrom the corresponding'salts, comprisingcharging the silicateinto a cage having a perfor at ed bottom and openat the top, disposed in the upper portionof a closed container, whilecharging the liquid, consisting of an aqueous solution of acid,'into thelower portion of the said container and heating it in order to obtainwet satu-',

rated acid vapour, permitting the same to pass throughthe mineral, whichis at a slightly lower temperature, the vapour thus condensed and sat:urated with the soluble s'alt'abstracted from the mineral dropping intothe hot liquid at the botexhausted or the underlying liquid has reachedsaturation of thesaid substances, including the furtherstep ofintroducing at the-end of the from said distillation to pass through thesaid fresh charge of; material, thereby utilizing the acid distilledfrom the liquid, and finally withiron and silica from said-container.

' jFitL JOURDANI tem of the'container, the cycle above describedbeingcontinued until the material is completely I

